Humans not alone in threatening other species with use of tools

Humans are not alone in the use of tools that threatens the livelihood of other species, scientists have found.

Oyster-eating monkeys in southeast asia are endangering the shellfish population in their habitat, thanks to their use of stone tools, an international team of scientists reported in the journal eLife.

Dr Lydia Luncz from Oxford University, the lead author of the study, speaking at the British Science Festival, said that “Tool use has allowed humans to become one of the most successful species. However, tool-assisted foraging has also pushed many of our prey species to extinction or endangerment, a technology-driven process thought to be uniquely human.”

Meet Thailand long-tailed macaques

Dr Luncz and her colleagues studied two groups of long-tailed macaques, which are the most recent species of monkey found to use stone tools, roaming on two neighbouring islands off east coast of Thailand called Koram and NomSao.

These macaques use choice stone tools to feast on shellfish. They handpick pointy stones to chisel off oyster shells, and flat-faced stones to hammer open sea snails.

Local shellfish population threatened

The size of shellfish, their availability, and the size of tools used to open them were all found to be smaller on the island with more macaques.

On the island Koram, which is densely populated with over 80 macaques, shellfish can be twice as small in size as those found on NomSao, which is sparsely populated with just 9 monkeys.

NomSao also has nearly three times as many sea snails as Koram.

The stone tools found on Koram are one third the size of those found on NomSao.

The findings suggest that once the population of macaques becomes sufficiently high, their use of tools results in a negative impact on the shellfish populations they prey on.

“We provide evidence that once technological macaques reach a large enough group size, they enter a feedback loop – driving shellfish prey size down with attendant changes in the tool sizes used by the monkeys.” Dr Luncz added.

Tool-using could be lost as a result

Scientists believe that without shellfish to prey on, the monkeys will also have no need to use the tools so might ‘unlearn’, eventually forget, how to use them altogether.

“With no need to use the stones for foraging, the technique might be lost. As this is a learned social behaviour, in the long term there will be a generation of macaques that do not know how to use tools, and any associated benefit will be lost.” Dr Luncz concluded.

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